Geomagnetism and Aeronomy

The influence of large-scale interplanetary structures on the propagation of solar energetic particles on August 27, 2022 is studied. The dynamics of particles fluxes, observed at the Lagrange point L1 and in the near-Earth space has a number of particular features, such as the synchronous local maxima of electron andproton fluxes of different energies during the flux growth phase and the anisotropy of the solar proton flux for about 12 hours. The time profiles of solar protons observed near the Earth are similar to those observed at L1 point, though with a delay of more than an hour. We suppose that the observed features can be explained by modulation processes during the propagation of particles inside the leading compression region ahead of the high-speed solar wind stream from the coronal hole.

Variations in the sunspot areas and indices, as well as the areas and magnetic fluxes of coronal holes are considered for the first five years of Cycle 25. The analysis is based on the source data from https://observethesun.com. The magnetic fluxes of coronal holes were calculated from the synoptic maps of magnetic fields obtained from two independent instruments: the Helioseismic and Magnetic Imager/Solar Dynamics (HMI/SDO) and the Solar Operational Prediction Telescope/Kislovodsk Mountain Astronomical Station of the Pulkovo Observatory (STOP/KGAS). The study of variations of the monthly indices and sunspot areas in both hemispheres revealed a pronounced asymmetry in the sunspot production rate during the period under consideration in favor of the southern hemisphere. In the same period, a significant asymmetry was also observed in the occurrence time and amplitude of polar and low-latitude coronal holes. At the beginning of the period from January 2020 to April 2022, the main contribution to the total area was made by polar coronal holes. Then, the contribution of low-latitude coronal holes dominated until the end of the period under consideration, although at certain moments the contribution of both types of coronal holes was significant. A comparative analysis of the dynamics of magnetic fluxes of coronal holes based on the HMI/SDO and STOP/KGAS synoptic maps for the same period (2014-2024) showed a good agreement between the results. This is a strong argument in favor of a regular use of domestic instruments, in particular STOP/KGAS, in studying the evolution of solar magnetic fields.

Fluctuations in the values of the IMF components of the solar wind plasma near the front of a fast reverse shock were analyzed using the WIND satellite data with a time resolution of 11 Hz. Two ways of dividing the magnetic field vector into components were considered: according to the GSE coordinate system and relative to the normal of the interplanetary shock front. It was found that the break frequency of the fluctuation spectrum of magnetic field components in the solar wind upstream region lies in the frequency range from 0.37 to 1.37 Hz. In the solar wind downstream region, the break frequency shifts to the range of 0.45–1.58 Hz, which corresponds to the scale of the proton inertial length. The slope of the fluctuation spectra of the IMF components was shown to vary both on MHD and on transient scales, although to different degrees. On transient scales, the difference can be significant.

The mean statistical dependence of the Dst-index on the heliospheric parameters during the development of storms initiated by solar coronal mass ejections (CME-storms) and corotating interaction regions (CIR-storms) is analyzed. It is found that the dynamics of the Dst-index and the β-parameter (equal to the ratio of the thermal pressure to the magnetic pressure) are qualitatively similar during the development of storms caused by CME and CIR flows. In the main phase of the CME- and CIR-storms, the mean statistical value of the β-parameter is β < 1 and β > 1, respectively, which manifests different plasma turbulence in the solar wind flows. It is shown that in the area of developing CME- and CIR-storm, the trajectory of Dst variation depending on the heliosphere parameters in the main phase of storms does not coincide with its trajectory in the recovery phase. This is a typical feature of the hysteresis phenomenon. The hysteresis effect between the Dst-index and the key parameters of the solar wind and interplanetary magnetic field (IMF) is observed during the development of both types of storms, indicating a nonlinear nature of the relationship between Dst and heliospheric parameters. The shape and size of the hysteresis loops vary depending on the analyzed parameters. The hysteresis loops for CIR-storms are smaller in area than those for CME-storms. It is found that in the period preceding the occurrence of CME- and CIR-storms, the solar wind flows have a closed configuration of the IMF intensity vector B in the ecliptic plane with different directions of the rotation.

A method was developed for detecting anomalous variations in the cosmic ray flux intensity during geomagnetic storms. The method involves cognitive rules for choosing solutions and is a synthesis of the threshold wavelet filtering and elements of the statistical decision theory. Numerical implementation of the method allows obtaining the best (in a certain statistical sense) solution at a rate of data receipt in the processing system. Data from ground-based neutron monitors of high-latitude stations (nmdb.eu) were used in the study. Two periods of extreme geomagnetic storms G5 and G4 accompanied by two deep Forbush decreases recorded on May 11, 2024 and January 01, 2025, were considered. The proposed method made it possible to detect anomalous changes in the intensity of the cosmic ray flux several hours before the onset of Forbush decreases and the registration of geomagnetic storms.

The processes that occur in the polar cap region and depending on the IMF By sign are considered. The paper describes the results of a comparative analysis of the distribution of field-aligned currents, auroral precipitation, ionospheric plasma convection, and electron density under conditions of northward IMF and the IMF By component of opposite signs. The field-aligned currents and precipitating particles are obtained from the AMPERE and DMSP satellite data. The convection patterns are obtained from the SuperDARN and numerical models; the electron density is calculated using the empirical IRI and regional numerical models. It is shown that the disturbances in the northern hemisphere are concentrated near the pole and differ significantly at opposite By signs. At By+, the precipitation intensity at the center of the polar cap is much higher than at By–. Moreover, only at By+ does the evening convective cell prevail over the morning one, providing a circumpolar flow of ionospheric plasma in a broader range of latitudes. The model electron density distribution in the polar cap shows the formation of a polar peak at By+ and a depletion at By–, which corresponds to the direction of field-aligned currents and the structure of precipitation. If By+, a ‘cyclone’-type structure is formed in the northern polar ionosphere, where the energy and momentum of the solar wind are effectively transferred to the ionosphere during several hours of the northward IMF.

The disturbances of the external magnetic field produced by a turbulent flow of a conducting incompressible liquid around a solid dielectric sphere are investigated. The fluid flow is calculated in the approximation of the RANS model, which takes into account the effects of turbulent viscosity. The COMSOL multiphysical simulation platform is used for numerical modelling of hydrodynamic and magnetic perturbations. The solution of the problem is obtained for an arbitrary orientation of the external magnetic field. The angular distribution and the decrease in amplitude of the magnetic disturbances with distance are studied numerically. The directions of maximum magnetic disturbances are determined. The area near the turbulent wake is investigated in detail. Approximate asymptotic laws of decrease of magnetic disturbances as a function of distance to the center of the ball are derived. The magnetic disturbances caused by laminar and turbulent regimes of the fluid flow around a sphere are compared.

An original approach to automatic classification of auroras by machine identification of images received from sky photo recorders, also known as all-sky imagers, is proposed. The total of 163899 sky images taken at 10-minute intervals within the auroral oval (Kola Peninsula, Russia) were selected over a 10-year period. We propose an intelligent information system designed to classify each acquired image into one of seven predefined categories. Analysis of the quality metrics of the system built on the basis on the ResNet50 neural network architecture showed the accuracy of the classification at the level of 96 %, which is practically unachievable when manually processing data samples of such a volume. The result of automatic classification of sky images based on the proposed system is available at the link: (https://disk.yandex.ru/i/76OMyWR4YyVYuw).

The Earth′s global seismic activity is analyzed to identify a possible impact of strong magnetic storms. We chose as the primary quantitative measure of the Earth's global seismic activity the total number of strong (magnitude M ≥ 5.0) crustal (hypocentral depth 0 ≤ h ≤ 60 km) earthquakes per day over the world (N_EQ). The geomagnetic activity and the strength of each particular magnetic storm were estimated based on the hourly values of the DST-index. Only strong geomagnetic storms that meet the condition DST_extr ≤ –150 nT were considered. The storm database under investigation includes only those events for which the final hourly DST values for the period from 1957 to 2016 are available. The modified superposed epoch method was used as the main analysis tool. The reference (zero) day was the day on which the minimum DST-value was recorded. It was found that on the day preceding the reference day (day minus 1), the Earth's global seismic activity decreases significantly as concerns the sudden commencement magnetic storms (MS_SC). On day zero, the situation is not as clear, but a certain increase in the Earth's global seismic activity is observed for the gradual commencement magnetic storms (MS_GRAD). Moreover, on day +7, the Earth’s seismic activity for such storms increases significantly. Possible physical mechanisms are proposed and discussed to explain this behavior of the global seismic activity of the Earth on the basis of extremely simplified quantitative estimates.